1. Field of the Invention
The present invention relates to an optical document reading apparatus, such as, for example, an electrophotographic copying machine equipped with a recirculation document handler (RDH) or recirculating automatic document feeder, of a type having dual functions of scanning a document to be copied with the optical system moved relative to the document and of scanning the document with the document moved relative to the optical system.
2. Description of the Prior Art
In order to avoid an inconvenience in a system, where a plurality of documents are desired to be copied, the operator has to place the documents one by one on a document support, the electrophotographic copying machine is often equipped with a so-called recirculating automatic document feeder unit. The recirculating automatic document feeder unit is operable in synchronism with the copying operation taking place in the electrophotographic copying machine to successively feed the documents and permits the electrophotographic copying machine to realize a function of copying images born on, for example, both sides of each, onto opposite sides of a copying paper. An example of such electrophotographic copying system is disclosed in, for example, the U.S. Pat. No. 4,218,128, issued Aug. 19, 1980, and U.S. Pat. No. 4,536,077, issued Aug. 20, 1985.
The electrophotographic copying machine equipped with the recirculating automatic document feeder unit is known to have two operational modes. When a copying operation is to take place with the document placed on the document support, the system assumes the first operational mode in which an illuminating device including an illuminator; such as a halogen lamp and reflecting mirrors, all disposed beneath the document support (within the electrophotographic copying machine), is driven at equal speed to scan the document. On the other hand, when the documents are successively transported by utilization of the recirculating automatic document feeder unit, while each document is turned around a transport device of right cylindrical shape, the system assumes, the second operational mode in which the illuminating device is held still at a predetermined exposure position adjacent the transport device to scan the document being transported. The predetermined exposure position is generally defined in the vicinity of one of opposite ends of the stroke of movement of the illuminating device.
Rays of light from the illuminating device are guided towards the document and are selectively absorbed in correspondence with an image born on the document. Rays of light reflected from the document are then guided towards a photosensitive surface of a photoreceptor drum through a plurality of reflecting mirrors and a zooming lens assembly. As is well known to those skilled in the art, the photoreceptor drum is supported for rotation in one direction past a plurality of processing stations including a charging station at which point a corona discharger for electrostatically charging the photosensitive surface of the photoreceptor drum is disposed; a developing station at which a developing unit is disposed for applying a toner material to develop an electrostatic latent image into a visible powder image; a transfer station at which a transfer corona discharger is disposed for facilitating the transfer of the visible powder image onto a copying paper; and a cleaning station at which residue toner material and residue electrostatic charge are removed from the photosensitive surface of the photoreceptor drum in readiness for the next cycle of the copying operation.
In the first operational mode, during which the copying operation is carried out while the document has been placed on the document support, control is made to permit the operation of the optical system, including the illuminating device, the reflecting mirrors and the zooming lens assembly, to have a synchronized relationship with the operation of the processing units disposed radially outwardly of, and in the vicinity of, the photoreceptor drum. On the other hand, in the second operational mode, during which the recirculating automatic document feeder unit is utilized, control is made to permit the operation of the processing units around the photoreceptor drum to have a synchronized relationship with the transport of the document effected by the recirculating automatic document feeder unit. In either case, a copy of acceptable quality can be obtained on the copying paper.
In the prior art electrophotographic copying apparatus of the type referred to above, a detector for detecting the illuminating device, is employed and disposed at each of the positions, which the illuminator device assumes during the second operational mode and the scan start position which the illuminator device assumes during the first operational mode. Where the switching is effected between the first and second operational modes, the illuminating device is moved to one of the positions detected by the respective detectors prior to the start of the copying operation. Accordingly, the change in operational mode in the prior art electrophotographic copying machine requires a certain length of time during which the illuminating device is moved from one position to another. Where such movement of the illuminating device takes place frequently, it has been found that a drive unit, including a drive motor for driving the optical system, tends to be run out quickly, shortening the service life of the electrophotographic copying apparatus. Also, the use of the plural detectors associated with the operational modes constitutes an increased manufacturing cost.